Georgi Kodinov d9e82ba86c Bug #36259 (Optimizing with ORDER BY) and bug#45828 (Optimizer won't ...

use partial primary key if another index can prevent filesort

The fix for bug #28404 causes the covering ordering indexes to be 
preferred unconditionally over non-covering and ref indexes.

Fixed by comparing the cost of using a covering index to the cost of
using a ref index even for covering ordering indexes.
Added an assertion to clarify the condition the local variables should
be in.

2009-07-07 15:52:34 +03:00

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